Sandbox

During the src_unpack, src_compile, src_test and src_install
phases, ebuild.sh operates inside a sandbox. This is a special environment
which attempts to help prevent badly written ebuilds (or ebuilds working with
badly written build systems) accidentally writing outside of permitted locations.

All packages must build correctly when sandbox is active. Packages must not
achieve this by using sneaky tricks to make sandbox warnings not show up
—
the
sandbox is there to ensure that binary packages will work correctly, and that
a badly written Makefile won't cause problems. Using addwrite is
generally not the correct solution.